Flapping wing micro air vehicles (FWMAV) have received a great deal of interest in the research community in the past decade. Researchers have developed and designed FWMAVs using numerous innovative materials and manufacturing techniques.
Control laws have been developed to govern the operation of flapping wing vehicles. Some designs use averaging theory to parameterize the varying wing kinematics on the vehicle forces and moments. This control strategy required at least four actuators. In those designs, two actuators were used to actively control the angle-of-attack, and two were required to drive each wing in the stroke plane. Other designs used a similar time-averaged approach to develop a longitudinal flight controller for a flapping-wing micro air vehicle. The control law was written in terms of the aerodynamic forces averaged over one wing-beat cycle. It was assumed that the mean forces could be controlled as desired; however, the relationships between the mean-aerodynamic forces and the wing kinematic parameters were not established. The Nano Hummingbird is an example of an operational flapping wing vehicle and control law that utilized three actuators.
A split-cycle constant period frequency modulation technique independently controls four degrees-of-freedom (DOF) with two physical actuators. By adding a bob-weight and third actuator, it is possible to independently control five DOF. The split-cycle technique may be modified to include a wing bias that provides independent five DOF control with only two physical actuators. It should be noted that the two actuator/five DOF technique is only applicable to configurations using actuators that are capable of being biased, such as piezoelectric devices, and is not applicable to direct current motor actuators.
Given that power to weight ratio is a critical element in FWMAV design, it is desirable to enable control over the greatest possible number of DOFs using the fewest actuators. One technique that has been proposed by researchers for controlling a FWMAV is split-cycle constant-period frequency modulation (SCCPFM). In this technique, each wing's upstroke and downstroke can have different velocities, resulting in the ability to generate non-zero cycle averaged drag forces. These drag forces provide the ability to control the fore/aft translation, roll, and pitch degrees-of-freedom of the vehicle. Unfortunately, by using this technique, it is not possible to generate fore/aft translation independent from pitch commands. Non-zero cycle averaged lift can also be produced by the wings, allowing control over the vertical and yaw degrees of freedom. Therefore, by utilizing SCCPFM, four independent degrees-of-freedom of the vehicle can be controlled.
As a result, there exists a need for an FWMAV activation and control method capable of yielding control over 6 independent DOFs.